Hello,

While Studying Statistics I read about pooled variance and it says “Pooled variance is a method for estimating variance given several different samples taken in different circumstances where the mean may vary between samples but the true variance is assumed to remain the same”. I wanted to know why we assume the variance to remain the same.

And also what is the difference between the standard error computed for two samples with and without Pooled variance.

where Sp= Pooled variance.

Thanks.